Preference circuit



July 30, 1968 H. HURVITZ PREFERENCE CIRCUIT Filed July 8, 1965 ATTORNEYSINVENTOR HYMAN HURVITZ m w t w 2 6 om R mmEUE United States Patent OhioFiled July 8, 1965, Ser. No. 470,411 6 Claims. (Cl. 841.19)

The present invention relates generally'to preference circuits, and moreparticularly to circuits for selectively connecting sources to a load,wherein selection of any one source prevents transfer of signal fromnon-preferred other "sources to the load. According to the invention, aplurality of high impedance sources may be connected at will to spacedpoints along a relatively high resistance, so that the sources areordered along the resistance, one terminal of each source being groundedand the other being unconnected with the high resistance, so that thesources are all normally out of circuit. A separate switch is providedfor at will connecting each source in circuit, i.e., to one of thepoints, thus completing a circuit between the connected source and load,which may be an amplifier with a high impedance input circuit. Eachselecting switch, when closed, causes completion of a grounding circuitfrom a point of the high resistance which is upstream from the connectedsource, as seen from the load. Thereby, if two or more of the sourcesare connected simultaneously, the upstream source will provide no signalto the load, since its output is bypassed to ground, while thedownstream source will provide signal to the load, since its output isnot so grounded.

In a known prior art system of the type under consideration, the sourcesthemselves were of low impedance and hence each source provided a groundcircuit for sources upstream of itself. However, the sources are thenrequired to be theoretically of zero impedance, which are difficult todesign, and to the extent the low impedances are not zero, cross-talkensues, i.e., signal from plural sources appear at the load. The presentinvention permits use of high impedance oscillators, yet eliminatescross-talk entirely, by providing low impedance paths externally of thesources themselves.

Where sources are mentioned, any source of oscillations is implied,including oscillators, frequency dividers, and the like, the inventionbeing independent of the character of the sources.

The present invention finds obvious application to root tone organsystems, wherein a tone is conveyed to an output system correspondingonly to the lowest note of a chord being played on an accompanimentmanual.

It is an object of the invention to provide a novel preference circuit,the design of which is flexible, so that the signals sources can be oflow or high impedance, as desired, but in which cross-talk is entirelyeliminated.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein:

The single figure of the drawing is a schematic circuit diagram of apreference circuit according to the invention.

In the single figure of the drawings, 10, 11, 12, 13 are exemplarysignal sources, such as oscillators. The sources -13 are assumed to beof high impedance and are shown connected each in a series with aresistance, as 14. The resistances 14 may be equal. The resistances 14are considered source output impedances. Single-pole singlethrowswitches 22, 23, 24, 25 are provided to selectively connect theungrounded terminals of sources 10-13, in-

elusive, to separate points 15-18, respectively, of resistance chain 20.

3,395,242. Patented July 30, 1968 Point 18 of resistance chain 20 isconnected to the grid 30 of an amplifier tube 31, having an anode load32 and a high grid leak resistance 33, say .5 megohm.

In operation, if only one switch is closed, voltage from only the oneassociated source will be present at grid 30. But if two of switches22-25 are closed, only'one of the two associated sources will providesuch voltage. If, for example, switch 25 and any other switch is closed,the source 13 associated with switch 25 will provide signal to grid 30but concurrently a zero impedance path from point 17 to ground will becompleted, and therefore the source connected by the other switch willnot affect the amplifier. As many switches as desired can'be closedsimultaneously and only that associated oscillator which is closest togrid 30 will provide signal thereto. All others are fully bypassed toground, but the preferred oscillator is isolated from ground by one ormore sections of resistance 20. I

Short circuit paths are provided from point 17' to ground via switch 40,closed when switch 25 is closed; via switch 41, closed when switch 24 isclosed; and via switch 42, closed when switch 22 is closed. It followsthat each downstream source, i.e., source most nearly adjacent to tube31, when connected in circuit, provides a zero impedance grounding pathfor all upstream sources. The grounding path is a dead short circuit, sothat crosstalk is totally avoided, and the grounding path is exclusiveof the source itself, so that source impedance is not a crucial factorin the operation of the present system.

Values of ladder network impedances and generator output impedances maybe such that:

(1) they are equal or approximately so,

(2) the network impedances exceed the generator output The signalpresent at the anode of tube 31 is applied via a conventional tone colorfilter 50, and amplifier 51, to a loudspeaker, or other electroacoustictransducer 52.. The switch pairs, as 25, 40 or 24, 41 or 22, 42 areactuated by the keys of a pedal clavier of an electronic organ, when thesystem of the invention is utilized in a pedal tone preference circuit,or by keys of an accompaniment manual, when utilized in a root tonesystem. A root tone system is a preference circuit, in principle, sinceonly the lowest frequency of a plurality of tones is raudibly calledforth when plural keys are actuated.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described mayberesorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What I claim is:

1. A preference circuit, including a plurality of resistances connectedin series,

a series of two terminal signal sources connectible each at one terminalto a different junction of said resistances, the other terminals of saidsignal sources being normally grounded,

separate switches for at will connecting each of said one terminal to aseparate one of said junctions,

a load circuit connected to one end of said plurality v of resistances,and

means responsive to closure of each of said switches for grounding apoint of said series of resistances lying outside the path connectingthe selected signal source to said load.

2. The construction according to claim 1 wherein said signal sources arehigh impedance signal sources.

3. A preference circuit comprising a,,series ofsignal sources arrangedin ordered array with respect to a load,

means for at will connecting any one or more of said signal sources tosaid load, and

means responsive to operation of said means for at will connecting forproviding a substantially zero impedance path to ground around all butone of said signal sources, whereby actuation of plural ones of saidmeans for at will connecting provides signal from only one of saidsignal sources at said load.

4L In an electronic musical instrument having a plurality of tonegenerators to generate electrical signals representative of musicaltones, and a tone signal response circuit to modify a characteristic ofat least one of the tones corresponding to one of said signals,

the combination with said tone generators and said signalresponse'circuit of a preference network of the character described,

said preference network having a ladder configuration and including animpedance element in each of the series arms of the ladder,

the impedance of the elements being of the same order of magnitude asthe output impedances of said tone generators,

switch means to connect the individual tone generators in the individualshunt arms of the ladder when the corresponding tones are selected to beplayed, and

a subsidiary circuit of negligible impedance for bypassing to ground allbut one of plural signals selected by said switch means.

5. In an electronic musical instrument having a plurality of tonegenerators to generate electrical signals representative of musicaltones, and a tone signal response circuit to modify a characteristic ofat least one of the tones corresponding to one of said signals,

the combination with said tone generators and said signal responsecircuit of a preference network of the character described,

said preference network comprising:

a plurality of impedance elements connected in series with one another,

A4 g each of said impedance elements having animpedance of the sameorder of magnitude as the output impedances of said tone generators,

switch means to connect the individual tone generators between theindividual junctions of said impedance elements and a common point orground when the corresponding tones are selected to be played, and.

a subsidiary circuit of negligible impedance for; bypassing to groundall but one of plural signals 'selected by said switch means. i

6. In an electronic musical instrument having a plurality of tonegenerators to generate electrical signals representative of musicaltones, and a tone signal response circuit to modify a characteristic ofat least one of the tones corresponding to one of said signals,

the combination with said tone generators and said signal responsecircuit of a preference network of the character described,

said preference network comprising: i

a plurality of resistors connected in series with one another, the valueof said resistors being of the same order of magnitude as the values ofthe output impedances of said tone generators,

a plurality of single-pole single-throw switches, one for each of saidtone generators, to connect the latter individually between theindividual junctions of said resistors and a common point or ground whenthe corresponding tones are selected to be played, and

a subsidiary circuit of negligible impedance for bypassing to ground allbut one of plural signals selected by said switch means.

References Cited UNITED STATES PATENTS ARTHUR GAUSS, Primary Examiner.

B. P. DAVIS, Assistant Examiner.

3. A PREFERENCE CIRCUIT COMPRISING A SERIES OF SIGNAL SOURCES ARRANGEDIN ORDERED ARRAY WITH RESPECT TO A LOAD, MEANS FOR AT WILL CONNECTINGANY ONE OR MORE OF SAID SIGNAL SOURCES TO SAID LOAD, AND